/Engine/Plugins/Runtime/nDisplay/Source/DisplayClusterScenePreview/Public/IDisplayClusterScenePreview.h
Set the root DisplayCluster actor for the renderer with the given ID, which will be added to the preview scene and used to determine the render world. Note that if the actor is destroyed (including by a recompile, reload, etc.), you will need to call this again to update the actor. This will also clear the path set by SetRendererRootActorPath.
bool SetRendererRootActor ( int32 RendererId, [ADisplayClusterRootActor](API\Plugins\DisplayCluster\ADisplayClusterRootActor) * Actor, bool bAutoUpdateLightcards )